Can a primordial magnetic field originate large-scale anomalies inWMAPdata?

Abstract

Several accurate analyses of the cosmic microwave background (CMB) temperature maps from the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed a set of anomalous results, at large angular scales, that appears inconsistent with the statistical isotropy expected in the concordance cosmological model cold dark matter. Because these anomalies seem to indicate a preferred direction in the space, here we investigate the signatures that a primordial magnetic field, possibly present in the photon-baryon fluid during the decoupling era, could have produced in the large-angle modes of the observed CMB temperature fluctuations maps. To study these imprints, we simulate Monte Carlo CMB maps, which are statistically anisotropic due to the correlations between CMB multipoles induced by the magnetic field. Our analyses reveal the presence of the north-south angular correlations asymmetry phenomenon in these Monte Carlo maps, and we use these information to establish the statistical significance of such phenomenon observed in WMAP maps. Moreover, because a magnetic field produces planarity in the low-order CMB multipoles, where the planes are perpendicular to the preferred direction defined by the magnetic field, we investigate the possibility that two CMB anomalous phenomena, namely the north-south asymmetry and the quadrupoleoctopole planes alignment, could have a common origin. Our results, for large angles, show that the correlations between low-order CMB multipoles introduced by a sufficiently intense magnetic field, can reproduce some of the large-angle anisotropic features mapped in WMAP data. We also reconfirm, at more than 95 per cent CL, the existence of a north-south power asymmetry in the WMAP 5-yr data.

Angular-planar CMB power spectrum

“…In what concerns deviations of isotropy, our analysis shows that the most anomalous scales are in the sectors (l, ) = (4, 7) and (6,8), where we can see that the points χ (2,3,4,5,6,7,8,9,10,11). Note that for xed l, the error bars do not oscillate (see the text for more details).…”

New constraints on the primordial magnetic field

“…Such a PMF could have influenced a variety of phenomena in the early universe such as the cosmic microwave background [18][19][20][21][22][23][24][25][26][27][28][29][30][31], non-Gaussianity and low multipole anomalies of the CMB [30,32,33], the formation of large-scale structure (LSS) [34][35][36][37][38][39][40], and the gravitational-wave background [41]. Effects of a PMF on the BB polarization mode of the CMB have also been studied by several authors [19,20,23,26,[42][43][44][45] and these effects have proven to be as important as the other physical processes which strongly affect the BB polarization through Lorentz symmetry violation [46][47][48].…”

Hemispherical power asymmetry: parameter estimation from cosmic microwave background WMAP5 data

“…Although the instrumental effects, like non-Gaussian and non-isotropic noise, or eccentric beams, and astrophysical foregrounds effects, like Galactic, and extra-Galactic point sources, and extended sources of emission, are either well controlled, or corrected for, or masked out, a set of an unexpected anomalies of various magnitudes and at various scales have been detected in the current CMB data (Abramo et al 2006;Bernui et al 2007a;Copi et al 2006aCopi et al , 2004Covi et al 2006;Cruz et al 2007;Destri et al 2008;Eriksen et al 2004;Land & Magueijo 2005a) (see also Cabella & Marinucci (2008); Huterer (2006); Martinez-Gonzalez (2008) for recent reviews and references therein). These anomalies call for plausible theoretical explanations since, if robustly detected, these can be used as valuable observables of the physics of the early Universe, or a new window on some of the late time effects (Akofor et al 2007;Bernui & Hipólito-Ricaldi 2008;Brown & Crittenden 2005;Destri et al 2008;Dvorkin et al 2008;Erickcek et al 2008;Inoue & Silk 2007).…”